In making can bodies for manufacturing cans for foodstuffs, tin plate is mostly used today in the range of thickness from 0.14 to 0.49 mm. Starting with a tin plate strip with a maximum width of 1200 mm, this is given an inner and outer lacquering as a rule and is cut into sheet metal plates. The regions of the later welded seams must be left free of lacquer during the lacquering, strip-shaped block-outs being provided, since the lacquer interferes with the roller resistance welding. Single can blanks are cut from the sheet metal plates, corresponding in their width to the can circumference and in their length to the can height. The geometry of the can blanks has to be taken into account already in the lacquering, so that the lacquer-free block-outs actually come to lie in the region of the welded seams. The can blanks are fed in a stack to a roller resistance welding machine, where they firstly undergo a flexing process in order to relieve internal stresses and are then bent into a cylinder. The beginning and the end of the cylinder which is formed are overlapped with an overlap width of 0.5 mm and the overlapping edges are welded together through the roller resistance welding. The cylinder thus resulting from the flat can blank forms the can body. The initially lacquer-free welded region is given a seam coating at least on the inside. After the welding the can body is given an edge bead at each of its two ends, to serve for the later attachment of a lid and a bottom. The can body is also given stabilising beads as a rule, in order to increase its external pressure stability for the later sterilising process of the filling material. Extensive re-tooling is necessary to set up different can diameters and different can heights, requiring relatively long re-tooling times. The can blank magazine, the flexing device and the bending apparatus have to be newly set up for this. A modification of the feed device is necessary for different can heights. A change in the can diameter requires fitting a matching welding arm. The result of the long re-tooling times is that the actual production times only amount to 50 to 70% of the possible time in use. In addition, the welding of the can body is not a continuous welding operation but the one body end represents the starting point and the other end the end point of the welded seam. Both points introduce sources of error on account of the discontinuous welding process, so that tears can occur here when edge-beading the can body.
The invention is therefore based on the object of providing a method of making can bodies from sheet metal for the manufacture of cans which facilitates cost-effective production of can bodies, with a high process reliability, through continuous welding.